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Anatomy of Pain

There are 3 well established factors that, taken together, provide overwhelming evidence of pain. [1]

1. Anatomical/ Neural Development

2. Behavioral Responses

3. Physiological Responses (the “Fetal Stress Response”)

18 Days Brain

The brain begins to take shape only 18 days after fertilization. By 20 days, the brain has already differentiated into forebrain, midbrain, and hind brain, and the spinal cord has started to grow. [2]

5 Weeks Pain Receptors

Four or five weeks after fertilization, pain receptors appear around the mouth, followed by nerve fibers, which carry stimuli to the brain. By 18 weeks, pain receptors have appeared throughout the body. Around week 6, the fetus first responds to touch. [3],[4]

6 Weeks Cortex

In weeks 6-18, the cerebral cortex develops. By 18 weeks the cortex has a full complement of neurons.  In adults, the cortex has been recognized as the center of pain consciousness. [5]

8 Weeks Thalamus

During weeks 8-16, the thalamus develops, functioning as the main relay center in the brain for sensory impulses going from the spinal cord to the cortex.[6] Movement of the fetus in response to external stimuli occurs at this early stage as well. [7]

14-18 Wks Nerve Tracts

In week 18, nerve tracts connecting the spinal cord and the thalamus are established, and nerves from the thalamus first contact the cortex in week 20. Nerve fibers not routed through the thalamus have already reached the cortex by 14 weeks. [8].[9]

18 Wks Stress Hormones

As early as 18 weeks, independent stress hormones are released by an fetus injected by a needle, just as they are when adults feel pain. Hormone levels in those babies decrease as pain-relievers are supplied.[10]  Painful stimuli also yield vigerous movements and breathing efforts.[11]

Before 18 Weeks?

Even before nerve tract s are fully established, the fetus may feel pain; studies show anencephalic infants, whose cortex is severely reduced if not altogether missing, may experience pain as long as other neurological structures are functioning.[12]

20 Weeks All Parts in Place

With pain receptors, spinal cord, nerve tracts, thalamus, and cortex in place, all anatomical links needed for pain transmission to the brain, for feeling pain, are present.  


[1] R Gupta, et. al. Fetal surgery and anaesthetic implications, Continuing Education in Anaesthesia, Critical Care & Pain. 2008 8(2):71-75.

[2] Blackburn, ST. Maternal, Fetal, and Neonatal Physiology. 2nd ed (2003).

[3] Ibid.

[4] Vanhatalo, S & van Nieuwenhuizen, O. “Fetal Pain?” Brain and Development. 22 (2000).

[5] Ibid.

[6] Blackburn, ST. Maternal, Fetal, and Neonatal Physiology. 2nd ed (2003).

[7] R Gupta, et. al. Fetal surgery and anaesthetic implications, Continuing Education in Anaesthesia, Critical Care & Pain. 2008 8(2):71-75.

[8] Vanhatalo, S & van Nieuwenhuizen, O. “Fetal Pain?” Brain and Development. 22 (2000).

[9] “Expert Report of Kanwaljeet S. Anand, MBBS, D.Phil.” Northern District of the US District Court in California. 15 Jan 2004.

[10] Giannakoulopoulos, X., Sepelveda, W., Kourtis, P., Glover, V.,& Fisk, N. (1994). Fetal plasma cortisol and B-endorphin response to intrauterine needling. Lancet, 77-81.

[11] Boris P, Cox PBW, Gogarten W, Strumper D, Marcus MAE. Fetal Surgery, anaesthesiological considerations. Curr Opin Anaesthesiol 2004; 39: 375-80.

[12] Van Assche, FA. “Anencephalics as Organ Donors.” Am J Obstet Gyn 163 (1990)